1. Field of the Invention
This invention relates to a fabrication method and a structure of an indium tin oxide (ITO) anode containing nickel points for an organic light emitting diode (OLED) to selectively light.
2. Description of the Prior Art
As known universally, an OLED (organic light emitting diode) has a structure and a manufacturing procedure simpler than those of an LCD nowadays. Moreover, an OLED can light itself and be combined with a flexible substrate, and has no limitation of viewing angle, low power consumption, high brightness and a short response time. Therefore, an OLED can potentially to be applied to all kinds of audio and video displayers, such as mobile audio, cell phone, MP3, digital camera, PDA, electronic book, back light source of LCD, television and source of white light etc.
FIG. 1 is a diagram of a conventional multi-layer OLED device, which is provided with an ITO (indium tin oxide) substrate 2 possessing an anode 4 that is mostly a transparent conductive electrode, and a hole transport layer (HTL) 6, a light emitting layer (LEL) 8 and an electron transport layer (ETL) 10 located orderly on the anode 4. Finally, a metallic cathode 12 is fabricated on the ETL 10 by vacuum vapor deposition to complete such a conventional multi-layer OLED.
When a positive bias is applied to the OLED, an electric field is to be formed in the OLED. By the time, the electron and the hole are respectively injected to the metallic cathode 12 and anode 4. The electron is to pass through the ETL 10 and the hole is to pass through HTL 6 after the electron and the hole have surpassed the energy barrier of the cathode interface and the anode interface respectively. Then, the electron and the hole meet at the LEL 8 to form a neutralized but excited electron-hole pair, which is to release photon energy by radiation and then, return to ground state. What is mentioned above is a process of electro-luminescence.
As a related conventional skill of OLED, U.S. Pat. No. 6,420,031 B1, titled as “Highly transparent non-metallic cathode”, employs ITO as a non-metallic layer and copper phthalocyanine (CuPc) as an electron-injecting interface layer. The electron interface with low resistance is formed only when the ITO is set in an organic layer but not when the organic layer is set on the ITO. The CuPc has advantages that: (1) it is used as a protection layer to keep an organic layer underlying from being damaged during the ITO sputtering process; and (2) it is used as an electron-injecting region so as to combine with The ITO layer to transport electron to a neighboring electron transporting layer. But, a highly transparent cathode applied to the OLED in the patent is insufficient to transport because it injects electron to the electron transporting layer without optimization and the materials used are not proper to present the whole range of colors.
As mentioned previously, an electric field is to be formed in the OLED when a positive bias is applied to the OLED. By the time, the electron and the hole are respectively injected to the cathode and the anode. And, the key factor obtaining high injection efficiency is that the electron and the hole must surpass the energy barrier of the cathode interface and the anode interface respectively. In addition, there is always a cross-talk problem for a conventional passive OLED panel circuit.